It is known from the prior art to make outer body shells for motor vehicles out of polymers. Outer body shells of this type are used, for example, as bumpers or front-end modules. The bumpers and/or front-end modules may have built-in functionalities, such as distance sensors, lighting means, license plate holders, or the like. In the coming years, it is expected that integrated radar transmitting/receiving units, in particular, will be used increasingly in motor vehicles for the detection of objects and/or pedestrians.
Depending on the installation constraints of the particular motor vehicle, the location for mounting such radar transmitting/receiving units can differ. Different types of mounting arrangements are known from the prior art.
It is advantageous to install the radar transmitting/receiving units behind a bumper, using a suitable mounting device. In this location, the radar sensor is protected from rocks and other debris. In addition, this location conceals the radar sensor, so that the ever important external appearance of the vehicles front-end is not adversely affected. Presently, different options for mounting radar sensors in the front-end of a motor vehicle are being tested, for example, behind the radiator grill or behind the license plate holder. For this type of mounting, the radar sensors are typically encapsulated or placed inside holding devices, so that the radar sensor arrangement and its associated circuitry is not subjected directly to environmental factors such as rain, snow, or wet/cold weather.
Holding devices of the aforementioned type have the disadvantage that the characteristics of the radar beam change as a result of weather conditions, such as moisture, ice or snow, potentially limiting object detection in the area in front of the vehicle. The article entitled “Autonomous Driving Approaches Downtown,” published in IEEE Intelligent Systems, Vol. 13, No. 6, in 1999, describes optical- or radar-based image-detection systems for motor vehicles which achieve a visualization of the objects (pedestrians, houses, vehicles, traffic signs, etc.).
In the publication VDI Kongress Berlin, September 2001, entitled “AKTIV-REVERSIBLE SCHUTZKONZEPTE ZUR ERFÜLLUNG DER FUSSGÄNGER-SCHUTZANFORDERUNGEN NACH EEVC WG 17” (in English, “Active Reversible Protection Concepts to Meet the Requirements of Protecting Pedestrians under EEVG WG 17”), the link between radar sensor object detection and the use of active pedestrian protection is disclosed. In addition, a generic test device is demonstrated that leads to the configuration of different sensor systems for an active-reversible protection concept. In particular, this reference discusses the use of so-called pre-crash sensors in connection with contact-film sensors, mounted on the outer shell of a front or rear bumper, which function to activate a pedestrian protection system. These concepts have the disadvantage that weather conditions such as snow, ice, or rain/wetness can influence the object image resolution of the radar signals, thereby preventing activation of the pedestrian protection in case of a threatening collision with a pedestrian. It is also known that weather conditions influence the radar signal characteristic and, within the framework of a subsequent dynamic image analysis, can lead to incorrect information concerning the area/zone to be scanned in front of the motor vehicle. As a result, the radar sensor detection as well as object detection are negatively influenced during weather conditions in which reliable operation of the device is absolutely necessary, for example, icy rain.
The publication “WERKZEUGE UND TESTVERFAHREN ZUR ENT-WICKLUNG UND ANALYSE VON ACC-SYSTEMEN” (in English, “Tools and Test Methods For Developing and Analyzing Adaptive Cruise Control (ACC) Systems”), Aachen Colloquium “FAHRZEUG UND MOTORENTECHNIK 2000” (in English “Vehicle and Motor Technology 2000”), lists test requirements for radar-based adaptive cruise control (ACC) sensor systems that are designed to be resistant to the influence of adverse weather conditions.
The use of radar-based ACC systems together with an intelligent speed control leads to the integration of the radar sensor unit and the transmitter/receiver module (TRM). The TRM modules are often made using MMIC technology, meaning silicon-based monolithic integrated microwave circuits. As compared to common Gunn diode technology, MMIC technology has the advantage of a higher component density for the installation and dismantling, as well as compatibility with additional adaptive sensor devices. The aforementioned radar sensors with integrated evaluation units are also affected by adverse weather conditions, which can result in signal attenuation/distortion. For example, radar-signal attenuation can be caused by icing up of the frontal region of the motor vehicle, in connection with dirt particles being embedded in the ice. The signal attenuation/distortion has a significant negative effect on the desired and/or required object detection and identification in a zone of approximately 100 m in front of the vehicle, for example, when using long-range radar (LRR). LRR operates with a frequency-modulated continuous wave radar technology (FMCW radar technology), with a linear modulated radar wave, in the frequency range of 76-78 GHz. Presently, hidden installation in a motor vehicle is realized by using a cover.